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Summary: Resume: Zusammenfassung Data collected in seven experiments in greenhouses or phytotrons were used to develop an empirical description of the phenology of populations of Galium aparine L. (cleavers). Cleavers from a hedgerow population were found to differ from cleavers from an arable population in their need for vernalization. Moisture regime and amount of light proved to be unimportant for the timing of flowering. Nutrition had some influence on the timing of flowering, but daylength and maximum temperature were most important in this respect. Both can be involved by summation of the product of daylength and the effective maximum temperature (°C above the base temperature of 5.3°C). The resulting descriptive formula enables relevant developmental rates of arable field populations to be predicted over a broad range of environmental conditions. The flowering date in the field of cleavers from an arable population could be correctly predicted for cohorts of plants emerging at different dates in two independent sets of data collected in England and The Netherlands, by using this summation (17300 °C* h between emergence and flowering). The temperature sum divided by 17300 can also be used as a developmental scale that governs the changes in patterns of carbohydrate partitioning. Although the development of the first whorls on cleavers is primarily related to the mean day temperature, the summation can also be used to describe the development of the first whorls. Phenologie des populations de Galium aparine L. de terres arables et des haies en relation avec les conditions pedoclimatiques Des donnees collectees dans 7 experimentations en serre ou en phytotron ont ete utilisee pour developper une description empirique de la phenologie des populations de Galium aparine L. (gaillet). Les gaillets issus d'une population de haie se sont reveles differents des gaillets issus d'une population de terre arable dans leur besoin de vernalisation. Le regime d'humidite et la quantite de lumiere n'a pas d'importance pour repoque de floraison. La nutrition a quelque influence sur l'epoque de floraison, mais la longueur du jour et la temperature maximale sont plus importantes k cet egard. Les deux peuvent etre impliquees par la sommation du produit de la longueur du jour avec la temperature maximale efficace (°C au-dessus de la temperature basale de 5,3). La formule descriptive qui en eesulte permet de prevoir les taux de developpement des populations en champs laboures sous un large eventail de conditions environnementales. La date de floraison au champ des gaillets issus d'une population de terre arable a pu etre correctement prevu pour des vagues de plantes levees k des dates differentes a partir de deux lots de donnees independantes collectees en Angleterre et aux Pays-Bas en utilisant cette sommation (17300°C* heure entre la levee et la floraison). La somme de temperature divisee par 17300 peut aussi etre utilisee comme une echelle de developpement qui regie les changements dans les schqui regie les changements dans les schemas de la partition carbohydrate. Bien que le developpement des premieres verticilles chez le gaillet soit principalement liea la temperature moyenne joumaliere, la sommation peut aussi etre utilisee pour decrire le developpement des premiers verticilles Phanologie von Feld- und Heckenpopulationen von Galium aparine L. je nach Witterung und Bodeneigenschaften Mit Ergebnissen aus 7 Versuchen im Gewachshaus oder Phytotron wurde eine empirische Beschreibung der Phanologie von Galium aparine (Kletten-Labkraut-) Populationen entwickelt. Kletten-Labkraut aus Heckenpopulationen unterschied sich von Feldpopulationen durch die Notwendigkeit der Vernalisation. Bodenfeuchtigkeit und Lichtin-tensitat erwiesen sich fur den Bluhbeginn als unwichtig. Dungung hatte einigen Einflus auf den Bluhbeginn, doch Tageslange und Temperaturmaxima waren dafur sehr wichtig. Beide Faktoren konnen als Summe des Produkts der Tageslange mit der effektiven Maximal-Temperatur (°C uber der Basistemp-eratur von 5,3 °C) einbezogen werden. Die daraus resultierende beschreibende Formel er-laubt es, rele van te Entwicklungsraten von Feld-populationen uber eine grose Breite von Umweltbedingungen zu prognostizieren. Das Bluhdatum einer Feldpopulation von Kletten-Labkraut konnte fur zu verschiedenen Zeiten in 2 unabhangigen Satzen keimende Pflanzen-gruppen, die in England und den Niederlanden gesammelt worden waren, durch Anwendung dieser Summe (17300°C* Stunden zwischen Keimung und Blute) korrekt vorhergesagt werden. Die Temperatursumme, geteilt durch 17300, kann auch als Entwicklungsskala genutzt werden, die die wechselnde Kohlen-hydratspeicherung umfast. Obwohl beim Kletten-Labkraut die Entwicklung des 1. Blatt-quirls hauptsachlich von der mittleren Tages-temperatur abhangt, kann dieses Stadium auch mit der Temperatursumme beschrieben werden.

Summary: Resume: Zusammenfassung The effect of nitrogen, phosphorus and potassium on the growth of weeds was studied at two locations on low-fertility acid soils in Suriname. Nitrogen stimulated the growth of weeds in terms of ground-cover and weight on a loamy sand of comparatively low fertility, as well as on a sandy loam of higher fertility. Phosphorus ultimately only stimulated ground-cover development and growth on the sandy loam, and interacted positively with nitrogen on that soil. Potassium had no effect on weed weight, but at both locations the number of plants increased with application of K. Differences in the amount of weed growth between the two locations were related to differences in the composition of the weed flora. On the sandy loam with application of 50 kg N, 50 kg P and 40 kg K ha−1, nutrient uptake by the weeds was 72 kg N, 10 kg P and 121 kg K ha− over a period of 35 days. Reponse des adventices a l'application d'azote, phosphore et potassium sur des sols pauvres acides au Surinam En deux lieux du Surinam avec des sols pauvres acides, l'effet de l'azote, du phosphore et du potassium sur la croissance des adventices a eteetudie. L'azote a stimule la croissance des adventices en terme de couverture du sol et de poids sur un sable limoneux relativement pauvre aussi bien que sur un limon sableux de plus grande fertilite. Le phosphore a finalement seulement stimule le developpement et la croissance sur le limon sableux et il y a eu une interaction positive avec l'azote. Le potassium n'a pas eu d'effet sur le poids des adventices, mais dans les deux situations le nombre de plantes a augmente avec l'application de K. Les differences dans la quantite de mauvaises herbes entre les deux situations etaient liees aux differences dans la composition de la flore adventice. Sur le limon sableux avec une application de 50 kg d'azote, 50 kg de phosphore et 40 kg de potasse a l'hectare, l'absorption par les adventices a ete en 35 jours de 72 kg N, 10 kg P et 121 kg K a l'hectare. Wirkung einer Stickstoff-, Phosphor- und Kaliumdungung auf die Verunkrautung ertragarmer, saurer Boden in Surinam An 2 Orten mit ertragarmen, sauren Boden in Surinam wurde die Wirkung einer Stickstoff-, Phosphor- und Kaliumdungung auf das Wachstum von Unkrautern untersucht. Stickstoff forderte das Wachstum von Unkrautern (Bodendeckung, Biomasse) sowohl auf einem verhaltnismasig ertragarmen lehmigen Sand als auch auf einem ertragreicheren sandigen Lehm. Phosphor forderte letzten Endes Deckungsgrad und Wachstum nur auf dem sandigen Lehm und wirkte da positiv mit Stickstoff zusammen. Kalium hatte keine Wirkung auf die Biomasse, aber an beiden Orten fuhrte es zu einer groseren Pflanzendichte. Die Wachstumsunterschiede an den beiden Orten hingen von der Zusammensetzung der Unkrautflora ab. Auf dem sandigen Lehm betrug bei 50 kg N, 50 kg P und 40 kg K ha−1 die Nahrstoffaufnahme der Unkrauter 72 kg N, 10 kg P und 121 kg K ha−1 innerhalb 35 Tagen.

The role of temperature in the regulation of seasonal changes in dormancy and germination was studied in seeds of Polygonum persicaria. Seeds were buried in the field and under controlled conditions. Portions of seeds were exhumed at regular intervals and germination was tested over a range of conditions. Seeds of P. persicaria exhibited a seasonal dormancy pattern that clearly showed the typical features of summer annuals, i.e. dormancy was relieved at low winter temperatures, the germination peak occurred in spring and dormancy was re-induced in summer. The expression of the dormancy pattern was influenced by the temperature at which germination was tested. At 30°C exhumed seeds germinated over a much longer period of the year than at 20° or 10°C. Nitrate added during the germination test occasionally stimulated germination. The seasonal changes in dormancy of buried seeds were regulated by the field temperature. Soil moisture and nitrate content did not influence the changes in dormancy. The fact that, on the one hand, field temperature determined the changes in dormancy and, on the other hand, germination itself was influenced by temperature, was used to describe the seasonal germination pattern of P. persicaria with a model. Germination of exhumed seeds in Petri dishes at field temperature was accurately described with this model. Germination in the field was restricted to the period where the range of temperatures over which germination could proceed (computed with the model) and field temperature overlapped.

After a brief historical survey of the developments of vegetation science in general, and of lichen community studies in particular, this paper presents critical comments on some of the main methodological problems in the study of lichen vegetation, with particular regard to the phytosociological approach. It is suggested that in the description and classification of lichen communities lichenologists should avoid the inflation of community names that characterize the present state of the phytosociology of phanerogamic vegetation. This can be accomplished on the basis of a sound methodological approach, where the use of numerical methods can play a major role.

A weed flora rapidly built up with the cultivation of annual crops on two experimental farms in the Zanderij area of Suriname, despite the fact that the farms were newly established in forested areas. Studies indicated that without adequate weed control, significant yield losses occurred in groundnuts, sorghum and soybeans due to competition with weeds. Plant density of the crops was not affected, but competition with weeds reduced ground-cover and leaf area index. Competition affected growth rates, leading to lower yields. The nature of the competitive effects is discussed and data are presented on the spatial distribution of weed growth in the crops. To prevent yield reduction in groundnuts and soybeans, competition during the period of pod initiation should be avoided. In sorghum, competition must be prevented during the period of floret establishment. In groundnuts, a period of 15 weed-free days after planting prevented yield loss and the presence of too much weed at harvest. Yield losses in sorghum were prevented with about 20 weed-free days after planting. A period up to around 30 days was needed to attain negligible weed growth at harvest. It was necessary to weed soybeans up to around 30 days after planting to avoid yield loss and too much weed growth at maturity. The response of weeds to fertilizer application varied, depending on the weed vegetation and the nutrient applied. Both stimulation of growth and increase in weed density were observed. Band-placement of fertilizers in planter press wheel furrows considerably reduced weed growth when compared with broadcast fertilizers.

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